Periods in The Periodic Table of Elements

Horizontal rows of elements from left to right in periodic table is called period. The periodical calendar is divided into seven distinct “periods.” It’s fascinating to see how pieces created around the same time have many of the same characteristics. The period containing the longest element is called the long period. The number of valence electrons of elements in same period increases gradually by one across the period from left to right. This leads to a parallel development of properties for element in each period (Katz, 2001).


1. First period

Often called the short period, the first period contains only two elements. These elements are Hydrogen and Helium. The two elements are separated from the other elements of the periodic table by atomic weight (Pyykko, 2012).


2. Second period

* This period is also called short period. Second period elements include beryllium, neon nitrogen, oxygen, fluorine, boron, nitrogen, lithium, and carbon. The octa condition holds true for the components of the second cycle. They can accommodate up to eight electrons in the 2p sub-shell. The elements of the second period also have an atomic weight that is one-quarter the weight of the elements of the first period.
* Those elements that belong to the second period of the periodic table display anomalous periodic properties. They have small radii and electron configurations that differ from the heavier congeners. These properties result from the occurrence of energetically unavailable d orbitals.
* The second period of the periodic table is represented by the elements of row two. These elements are mostly metals, although some non-metals are present as well. The elements in the second period obey the octet rule. There is no electron in the third shell, and there are a maximum of eight electrons in the second shell (Xia & Yanai, 2019).


3. Third period

• This period is also called short period. It contain eight elements. This include sodium magnesium aluminum silicon phosphorous sulphur chlorine and astatine. Having an understanding of Period 3 elements and their properties is important. Period 3 elements are the third row of the periodic table. These elements represent their own group’s properties without any anomalies.
• Period 3 elements have an overall upward trend. As time progresses, more and more protons and electrons are created. These elements generally react to produce a stable “octet” of electrons.
• Atomic size is also an important property of elements. Measured from the center of the nuclei to the edge of the atomic shell, this is known as the atomic radius. When the outermost electrons shell is magnetized, it attracts the nucleus more strongly. This effect increases the first ionization energy of the element.
• The number of valence electrons also increases as the period goes along. The atoms have more electrons than they did in the first period, which helps to make them more resistant to losing electrons.


4. Fourth period

• This period is also called long period. Elements in this period are potassium calcium scandium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton. Fourth period contains 18 elements. These elements all have valence electrons that enter the fourth energy level of the valence shell. These elements are the heaviest elements.
• Period 4 contains a variety of elements that play important roles in the function of proteins. Calcium is a seven metal and plays a critical role in skeletal muscle contraction in vertebrates. Eukaryotes use manganese enzymes. Calcium also plays a crucial role in maintaining membrane potential and neurotransmitter firing.


5. Fifth period

This period is also called long period .The fifth period is filled with 18 elements. These include the alkali metals (such as rubidium strontium), the transition metals (such as yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine and xenon. This period also contains the d-block elements (Katz, 2001).


6. Sixth period

• Currently, the sixth period contains 32 elements. To put it simply, it’s the longest duration in the table. The period is composed of the transition metals. These are metals that occupy short columns between Group 2A and Group 3A. These metals are sometimes called B-group elements.
• During the sixth period, the elements of the periodic table are represented by the lanthanides. The lanthanides are also known as rare earths. Some of them have very special properties, like magnetic properties. They are also considered transition metals. They are very soft and silvery, and they oxidize at high temperatures.


7. Seventh period

Often referred to as the longest period, the seventh period contains 32 elements and is often compared to the sixth period, which is a tad shorter .Actinides are present in this period (Pyykko, 2012).


8. Characteristics of period in periodic table


Important characteristics of periods are given below (Xia & Yanai, 2019).


8.1. Valence electrons

Valence electrons are the electrons in the outermost shell of an atom. They determine the chemical properties of an element and are involved in a number of chemical processes. They also have a role in electric current in semiconductors. Depending on where it stands in the periodical table, an element’s valence electrons count may vary. From one to 8 electron pairs are typically found in the least frequent elements. It’s true that there are a few outlier.


8.2. Valency

Valency is a concept that is used to predict the chemical properties of a compound. Additionally, it aids in comprehending how various molecules interact with one another. One of the cornerstones of chemistry is the idea of valency. Understanding this concept can help in creating new compounds.


8.3. Metallic character

Typical metallic properties include high electrical conductivity, high thermal conductivity, ductility, malleability, and high tensile strength. Other properties include the ability to displace hydrogen from dilute acids, halide compounds, and halogens. Metallic properties tend to decrease across each period while non-metallic properties tend to increase.



During the 19th century, a Russian chemist named Mendeleev discovered the periodic table. He presented his findings to the Russian Chemical Society in 1869. Using a combination of valence electrons and atomic weight, Mendeleev arranged elements by atomic number, atomic weight and valence electrons. This table helped chemists identify the elements that would be most suitable for specific processes.



1. Katz, G. (2001). The periodic table: an eight period table for the 21st centrury. The Chemical Educator, 6(6), 324-332.
2. Pyykko, P. (2012). The physics behind chemistry and the periodic table. Chemical reviews, 112(1), 371-384.
3. Xia, B., & Yanai, I. (2019). A periodic table of cell types. Development, 146(12), dev169854.